Process for converting coal into fuel cell quality hydrogen and sequestration-ready carbon dioxide

ABSTRACT

A process for burning coal to produce substantially pure hydrogen for use in fuel cells, together with “sequestration ready” carbon dioxide and a stream of oxygen depleted air for powering gas turbines, characterized by using a combination of two fluidized bed reactors and a third transfer line reactor, the first reactor being supplied with coal particles or “char” and fluidized with high temperature steam; the second reactor being fluidized with high temperature steam and the third reactor being fluidized by compressed air. Solids circulated among these three reactors include a mixture of materials containing calcium compounds (present as CaO, CaCO 3  and mixtures thereof) and iron compounds (present as FeO, Fe 2 O 3  and mixtures thereof). The coal is gasified by the steam in the presence of CaO to produce CaCO 3  and relatively pure hydrogen for use in fuel cells per a CO 2  acceptor process. Because only part of the coal char input to the first reactor is gasified to produce hydrogen, the remainder can be burned to supply thermal energy necessary to regenerate the CaCO 3  back to CaO. Carbon in the middle bed fluidized bed reactor reacts with Fe 2 O 3  in the third reactor and the temperature in the middle fluidized bed reactor is sufficiently high to decompose CaCO 3  back into CaO.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for convertingcoal, air and high temperature steam into three separate gas streams—oneconsisting of wet, substantially pure hydrogen, a second containing“sequestration-ready” carbon dioxide, i.e., CO₂ that is relatively pureand is at an elevated pressure thereby rendering its disposal lessdifficult, and a third stream consisting of oxygen depleted air.

More particularly, the invention relates to a process in which mixturesof coal, calcium and iron compounds are circulated among multiplereactors charged with either high temperature steam or compressed airthat produce essentially pure hydrogen for use in fuel cells as aproduct of a controlled gasification reaction. The process according tothe invention results in a separable and substantially pure carbondioxide waste stream having residual amounts of sulfur dioxide, and anoxygen depleted air stream having high temperature heat that can beused, for example, in downstream power generation subsystems. Theoxidation/reduction reactions of the present invention are much morethermodynamically efficient than conventional fossil fuel mixedcombustion systems and offer significant environmental advantages overprior art processes using coal or other fossil fuels or biomass fuels togenerate heat and combustion gases for use in gas turbine engines.

During the 21^(st) century, the United States will continue to relyheavily on fossil fuels, such as natural gas, oil and petroleumdistillates, as the primary source of fuel for gas turbine engines usedto generate electrical power. Recently, the use of substantially purehydrogen in fuel cells has been found to be more efficient and virtuallypollution-free as compared to other conventional fossil fuel/aircombustion technologies. Hydrogen fuel cells would be an ideal solutionto many of the nation's energy needs as a clean-burning fuel source.However, the need exists for a thermodynamically-efficient andeconomical process capable of producing large amounts of pure hydrogenfrom a readily available and inexpensive energy resource such as coal.

Various conventional systems exist for oxidizing (burning) coal togenerate free hydrogen in addition to producing heat for generatingsteam. Invariably, such systems pose significant environmental problemsbecause of the potential release of oxidized carbon and sulfur compoundsinto the atmosphere from burning coal. Conventional hydrogen generatingmethods also involve high equipment costs due to the inefficienciesinherent in attempting to recover and isolate hydrogen from the otherproducts of fossil fuel/air combustion.

It is al so well known that the carbon dioxide resulting from coal-firedsystems contributes to the greenhouse effect in the atmosphere andpotential global warming. Other types of air pollution produced by coalcombustion include particulate emissions, such as fine particles of ashresulting from pulverized coal firing, as well as the release ofundesirable oxides of nitrogen, chiefly NO and NO₂.

Thus, a significant need exists to produce relatively pure free hydrogenfor use in electrical power generation in an economical andthermodynamically efficient manner, but without polluting theatmosphere. The need also exists to control the nature and extent of anycarbon dioxide, and sulfur dioxide emissions created during coalcombustion by isolating and disposing of the oxidized contaminantswithout releasing them into the atmosphere. Ideally, coal and otherfossil fuels could be used to generate heat in a manner that allows theby-products of combustion, particularly CO₂, to be readily andeconomically recovered at elevated pressure and in a relatively purestate, i.e., making the CO₂ “sequestration-ready.”

In the past, a number of different CO₂ disposal methods have beenproposed such as pumping liquid CO₂ into deep parts of the ocean.However, one recurring problem in the disposal of CO₂ concerns thepurity of the waste stream itself. Since most disposal options involveliquid CO₂, it is generally accepted that for CO₂ to be“sequestration-ready,” it cannot contain more than small amounts ofimpurities or other gases that do not liquefy under pressure.

In addition to air pollution problems, the combustion of coal to drivegas turbine engines suffers from the same limitations in thermodynamicefficiency inherent in all systems that rely on mixed (air) combustionof coal as the primary heat source. Gas turbines are considered to beamong the lowest capital cost systems available for generatingelectrical power. However, their thermodynamic efficiency is notablylower than other systems. Although the efficiency increases withincreasing turbine inlet temperature, the hot gases produced by coalfiring contain fly ash which can be erosive to turbine blades. Thehigher temperature exhaust vapors can also be corrosive because of theacidic by-products of coal combustion, such as sulfur dioxide and HCl.Consequently, the maximum turbine inlet temperature that can betolerated for coal firing is considerably lower than that associatedwith a “clean” fuel, such as oil or natural gas.

Over the years, some improvements in gas turbine metallurgy haveincreased the inlet temperatures that could be tolerated with coal-firedsystems. By definition, the same technological advances serve toincrease the inlet temperatures for cleaner fuels such as natural gas.Thus, the disadvantages of coal relative to cleaner fuels remainregardless of the gas turbine metallurgy involved and prevent coaldespite its lower cost from being considered an attractive gas turbinefuel. The gas turbine industry has long recognized that if a processcould be developed for burning coal in a manner that produced largequantities of relatively “clean” hot gases that were not erosive orcorrosive, coal could become a much more economically viable fuel sourcefor use in electrical power generation.

One proposed solution to the problem of using coal to power gas turbinesis a process known as “gasification” in which coal and steam are fed toa high temperature reactor vessel and react to form a mixture of H₂, COand CO₂. Because the gasification reaction is endothermic, heat must besupplied in some manner. Thus, in most gasification designs, air ismixed with the high temperature steam so that a portion of the coalburns while the remainder reacts with steam to form H₂, CO and CO₂. Inother designs, a portion of the fuel solids are heated by combustion andthen mixed with coal and steam to supply the heat needed to drive thegasification reaction forward.

The literature describes a coal gasification process in which a CO₂acceptor (either limestone or dolomite) circulates between a pair offluid beds, one fluidized with steam and the other with air. See G. P.Curran, C. E. Fink, and E. Gorin (Chapter 10 in FUEL GASIFICATION, ACSAdvances in Chemistry series 69, 1967). The temperature in thesteam-fluidized bed remains low enough so that the CaO+CO₂═CaCO₃reaction gasifies coal to virtually pure hydrogen. Only part of thecarbon in the coal, however, becomes gasified in the steam fluidizedreactor. The remainder moves to an air fluidized bed where it isoxidized (“burned”), liberating heat and decomposing the CaCO₃ back intoCaO. Since the CO is in equilibrium with the CO₂ via the well-knownwater gas shift reaction, removal of the latter removes the former. Thebasic gasification process has the advantage of producing relativelypure hydrogen, but suffers from a disadvantage in that the CO₂ isreleased directly into the atmosphere along with air and other oxidizedby products of coal combustion such as sulfur dioxide.

U.S. Pat. Nos. 5,339,754; 5,509,362; and 5,827,496 (incorporated hereinby reference) disclose a method for burning fuels using a catalyst thatcan be readily reduced when in an oxidized state, and then readilyoxidized when in a reduced state. The fuel and air are alternatelycontacted with the catalyst. The fuel reduces the catalyst and isoxidized to CO₂ and water vapor. Thereafter, the air oxidizes thecatalyst and is depleted of oxygen. Thus, combustion is effected withoutthe need to mix the fuel and air either prior to or during thecombustion process. If means are provided whereby the CO₂, water vaporand oxygen-depleted air are directed in different directions as theyleave the combustion process, mixing can be completely avoided. Thislater method of combustion has been called “unmixed combustion.”

The total volume of combustion gases produced by unmixed combustion iscomparable to that produced in conventional combustion, but with onesignificant difference. The volume of the CO₂+water vapor steamrepresents only a small part of the total. As those skilled in the artwill appreciate, the cost of removing acid gases from combustioneffluents by scrubbing increases with the volume of gas being scrubbed.Thus, if unmixed combustion can be accomplished such that the acid gasesleave the combustion process in the form of a CO₂+water vapor steam, thevolume of gas that must be scrubbed can be substantially reduced, with acommensurate lower operating cost. As detailed below, operating unmixedcombustion in a manner such that the acid gases leave the combustor inthe CO₂+water vapor steam requires an appropriate choice of catalyst andclose control over the initial combustion reaction and subsequentdecomposition reaction.

The subject matter of the '362 patent is discussed in detail in a paperpresented at the Oct. 26-27, 1998 meeting of the Western States Sectionof the Combustion Institute (Paper No. 98F-36). The paper discloses ahypothetical process for using coal to power a gas turbine and reportson a series of preliminary experiments using an atmospheric pressurefluid bed of powdered chemically pure iron oxide (i.e., FeO/Fe₂O₃). Thegas used to fluidize the bed can be switched from air to 5% SO₂+95% N₂balance and back again. The experiments involved two basic processsteps. In the first step, a bed fully oxidized to Fe₂O₃ was fluidizedwith the 5% SO₂+95% N₂ at a temperature of 857° C. A small amount ofcoal was then injected into this bed while the gases coming out of thebed were continuously analyzed. In a second step, the fluidizing gas wasswitched to air while continuing to analyze the gases coming from thebed.

The Combustion Institute paper also proposes a conceptual design for aprocess to use coal to power a gas turbine. As shown in FIG. 4 of thepaper, the FeO/Fe₂O₃ catalyst is used as a fluidized powder whichcirculates between a first fluid bed fluidized with steam and a secondbed fluidized with compressed air from the compressor section of a gasturbine. Within this bed, FeO is oxidized to Fe₂O₃—a strongly exothermicreaction that depletes the compressed air of oxygen while heating theair. The heated compressed air (now oxygen-depleted) can then be used todrive the expander section of a gas turbine. The Combustion Institutepaper contemplates using pulverized coal as the main fuel source. SeeFIG. 4.

Thus, the prior art contains separate teachings of means for achievingthe goal of oxidating coal to sequestration-ready CO₂ and of means forachieving the goal of gasifying of coal to relatively pure hydrogen. Theprior art, however, does teach, show or suggest means for achieving boththese goals in the same process. A definite need exists for an improvedmethod of burning (oxidizing) coal using unmixed combustion to producesequestration-ready CO₂, relatively pure hydrogen while at the same timecreating a hot gas stream for use in generating electrical power byexpansion through gas turbine engines.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a new process for burning coal to producehydrogen for fuel cells, oxygen depleted air for powering gas turbines,and sequestration-ready CO₂. The process operates at conditions suchthat all of the chemical reactions involved are thermodynamicallyfavorable and readily occur and in a manner such that the process has aheat balance consistent with a practical industrial application.

In the preferred exemplary embodiment of the invention, two bubblingfluidized bed reactors and a transfer line reactor are utilized incombination. The first fluidized bed reactor (referred to herein as the“coal gasification reactor”; see Table 1) operates at 800° C., and issupplied with coal particles or “char” and fluidized with hightemperature steam, e.g., superheated steam at a pressure of about 7 Atm.The second fluidized bed reactor (called the “CaCO₃ decompositionreactor”) is also fluidized with steam and operates at about 1040° C.and 7 Atm. The third “FeO oxidation reactor” uses compressed air atabout 7 Atm. and reaches an operating temperature of about 1525° C.Solids circulated among these three reactors include a mixture ofmaterials containing calcium compounds (present as CaO, CaCO₃ andmixtures thereof) and iron compounds (present as FeO, Fe₂O₃ and mixturesthereof)

In the first fluidized bed reactor, coal is gasified by the steam in thepresence of CaO to produce CaCO₃ and relatively pure hydrogen (for usein, e.g., fuel cells) per the CO₂ acceptor process described above. Onlypart of the coal char input to the gasification reactor, however, isgasified to produce hydrogen. The remainder of the coal char is burnedto supply thermal energy necessary to regenerate the CaCO₃ back to CaO.The solids are circulated between the gasification reactor and themiddle fluidized bed reactor where they mix with solids from thetransfer line reactor. Carbon in the middle bed fluidized bed reactorreacts with Fe₂O₃ in the transfer line reactor and the temperature inthe middle fluidized bed reactor is sufficiently high to decompose CaCO₃back into CaO.

Thus, the solids recirculating out of the middle fluidized bed reactorconsist mainly of CaO and FeO, while gaseous CO₂ and minor amounts ofSO₂ are removed in a separate stream. Some of the solids mixture returnsto the first fluidized gasification reactor and the remainder passesinto the transfer line reactor. (FeO oxidation reactor). In the latter,FeO reacts with air in an endothermic reaction to liberate heat. The hotoxygen depleted air leaves the transfer line reactor and is supplied tothe gas turbine while the hot solids return to the middle fluidized bed.

Because the reaction between FeO and hot air is rapid and exothermic (inthe range of −292 kJ/mole), the temperature of the vitiated airincreases to a point that the hot gas can be expanded across a turbineto provide shaft power for electricity and/or drive the air compressor.Excess enthalpy from the expanded and vitiated air can also be recoveredby a boiler that provides high-pressure steam for use in thefluidization.

The gas stream leaving the FeO oxidation reactor normally passes througha cyclone or other hot gas cleanup system to remove ash and elutriatediron oxides before being expanded across a turbine. The hot gases fromthe CaCO₃ decomposition reactor can also be passed through a heatexchanger followed by a condenser to remove water and residual finesolids. The remaining gases consist of CO₂ and SO₂ at elevated pressure,with small amounts of other pollutants and products of incompletecombustion. The SO₂ and other pollutants can be removed by wet scrubbingor other treatment, leaving an essentially pure stream of pressurizedCO₂ for sequestration or discharge.

Accordingly, in its broader aspects, the invention relates to a processfor converting coal into fuel cell quality hydrogen and substantiallypure, i.e., sequestration ready, carbon dioxide in a much morethermodynamically efficient manner using solids mixtures containingcoal, calcium compounds and iron compounds circulating among threefluidized bed reactors operating simultaneously.

In another aspect, the invention relates to a new method for achievingthe unmixed combustion of coal to produce fuel cell quality hydrogen andsequestration-ready carbon dioxide waste using first, second and thirdreactors whereby the first reactor receives inputs of coal and steam toproduce an output gaseous stream of wet hydrogen gas, the second reactorproduces an output stream of wet carbon dioxide and the third reactorreceives an input stream and produces an output stream ofoxygen-depleted air.

In yet another aspect, the invention relates to a new apparatus forperforming the unmixed combustion of coal to produce substantially purehydrogen, carbon dioxide and oxygen-depleted air consisting of a first,second and third reactors with solids circulating among the reactorscontaining a carefully-controlled balance of calcium compounds andmixtures thereof and iron compounds and mixtures thereof.

In still a further aspect, the invention relates to a new unmixedcombustion apparatus capable of producing an output gaseous stream ofwet, fuel cell quality hydrogen gas, substantially pure, i.e.,“sequestration-ready” carbon dioxide and oxygen depleted air in a muchmore thermodynamically efficient manner than conventional unmixedcombustion systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the basic components andprocess according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically an exemplary embodiment of the invention thatconverts input streams of coal, steam and compressed air into separateoutput streams of relatively pure hydrogen for use in, e.g., fuel cells,sequestration-ready CO₂, and high temperature oxygen depleted air foruse in powering a gas turbine to produce electricity. In thisembodiment, two bubbling fluidized bed reactors 10, 12 are used togetherwith transfer line reactor 14. The first fluidized bed reactor 10 on theleft in FIG. 1 (the coal gasification reactor) is fluidized with a gasconsisting primarily of high pressure superheated steam via inlet 16 atthe bottom of the reactor.

The bubbling bed 12 in the center of FIG. 1 (the CaCO₃ decompositionreactor) likewise is fluidized with a gas consisting of superheatedsteam via inlet 18 or recycled CO₂ or mixtures thereof. The transferline reactor 14 (the FeO oxidation reactor) is fluidized with compressedair via inlet 20. The solids that circulate among these three reactorsinclude a mixture of solids, some of which have a high content of CaCO₃when in an uncalcined state, e.g., limestone and dolomite, and some ofwhich have a high iron content, e.g., iron ore, purified iron oxide, redmud, and pulverized scrap iron.

In the leftmost of the three reactors shown in FIG. 1, coal 22 entersthe fluidized bed at 24 and becomes gasified by steam in the presence ofCaO to produce CaCO₃ and relatively pure hydrogen per the CO₂ acceptorprocess described above. The hydrogen leaves the first fluidized bedreactor via stream 26 for use in hydrogen fuel cells.

Significantly, in the CO₂ acceptor process, only part of the coal charinput to the gasification reactor 10 is gasified to produce hydrogen.The remainder is burned to supply the thermal energy necessary toregenerate the CaCO₃ back into CaO. That is, heat from burning part ofthe coal is used to decompose the CaCO₃ back to CaO, however thecombustion is done indirectly. Solids are circulated between thegasification reactor 10 and the middle fluid bed CaCo₃ decompositionreactor 12 where they mix with solids from the transfer line reactor 14.Carbon in the former reacts with Fe₂O₃ in the latter. The temperature inthe middle or second fluidized bed reactor 12 remains high enough sothat CaCO₃ decomposes back to CaO. Thus, the solids recirculating out ofthe middle fluid bed reactor consist mainly of CaO and FeO while“sequestration ready” CO₂ (and any residual SO₂ present) leave themiddle fluidized bed reactor via stream 28.

Part of the mixture of solids returns to the gasification reactor 10 andthe remainder goes to the transfer line reactor 14. In the transfer linereactor 14, FeO reacts with air to liberate heat. Hot, oxygen depletedair exits the line reactor 14 via stream 30 and may be supplied to a gasturbine, while the hot solids return to the middle fluidized bed reactor12.

EXAMPLE 1

Computational experiments were done with the HSC program. Thecomputational procedure is an iterative one in which initialtemperatures are assumed for both of the bubbling bed reactors and thetransfer line reactor. Equilibrium product compositions are calculatedat those temperatures. The heat and mass balances are then calculated toproduce a new set of operating temperatures and the process is repeatedto obtain results mutually consistent within a reasonable margin oferror.

Computational experiments of this type produce three different types ofresults. The calculational procedure can fail to converge, showing thatthe process being studied is not capable of adiabatic operation.Alternatively, the calculations can converge showing that the process iscapable of adiabatic operation but under conditions in which thechemical equilibrium will not result in a practically useful process.Third, the calculations can converge to a result showing that theprocess being studied is capable of adiabatic operation at conditionsunder which the chemical equilibrium will yield a practically usefulprocess.

In doing the above calculations, the computer program assumes thatCaO/CaCO₃, and FeO/Fe₂O₃ act as perfect catalysts, i.e., all theCaO/CaCO₃, and FeO/Fe₂O₃ present reacts to equilibrium. It is, however,well known that catalysts in general have a finite life, i.e., theyslowly tend to become inert. To maintain an acceptable level ofcatalytic activity, the general practice is to continually remove andreplace small amounts of the catalyst. For catalytic processes thatinvolve coal, there is the added complication that coal contains ash.While conditions can be adjusted so that most of this ash exits thereactor as fly ash some will inevitably remain behind. This makesnecessary continual remove and replacement of small amounts of thecatalyst.

Thus, in practical operation, the reactors in accordance with theinvention will contain a mixture of active catalysts and inert solids.In order to take this factor into account, it was assumed that thecatalyst was a mixture of CaO/CaCO₃, FeO/Fe₂O₃, and Al₂O₃, the latterbeing an inert solid, with well known thermal properties. A smallportion of the CaCO₃ is also treated as inert.

Tables 1, 2, 3, 4 and 5 below show the results of the computationalexperiment.

TABLE 1 Mass Balance for Conversion of Coal, Steam, and Air into unmixedHS, CO₂ and O₂ Depleted Air Coal Gasification Reactor, 800° C., 7 atm.Input Reactants: 3.2H₂O at 500° C. and 1.79C at 25° C. Input Solids fromCaCO₃ Decomposition Reactor: 2.0FeO, 1.5Al₂O₃, 0.8CaO Output Solids toCaCO₃ Decomposition Reactor: 2.0FeO, 1.5Al₂O₃, 0.01CaO, 0.79CaCO₃, 1.0COutput Reaction Products: 1.58H₂, 1.62H₂O, traces of CO₂, CO and CH₄CaCO₃ Decomposition Reactor, 1042° C., 7 atm. Input Reactants: NoneInput Solids from Coal Gasification Reactor: 2.0FeO, 1.5Al₂O₃, 0.01CaO,0.79CaCO₃, 1.0C Input Solids from FeO Oxidation Reactor: 4.0FeO,3.0Al₂O₃, 1.6CaO Output Solids to Coal Gasification Reactor: 2.0FeO,1.5Al₂O₃, 0.8CaO FeO Oxidation Reactor, 1526° C., 7 atm. InputReactants: 1.0O₂, 4.0N₂ Input Solids from CaCO₃ Decomposition Reactor:4.0FeO, 3.0Al₂O₃, 1.6CaO Output Solids to CaCO₃ Decomposition Reactor:2.0Fe₂O₃, 3.0Al₂O₃, 1.6CaO Output Reaction Products: 4.0N₂

TABLE 2 Energy Balance for Conversion of Coal, Air and Steam intoSeparate Streams of H₂, CO₂ and Oxygen Depleted Air Sensible Heat, −ΔHof Combustion, kcal kcal Inputs C, 1.79 moles at 25° C. 0 −168.339 H₂O,3.2 moles at 500° C. 12.966 0 O₂, 1 mole at 500° C. 3.628 0 N₂, 4 molesat 500° C. 13.581 0 Totals 30.175 −168.339 Outputs H₂, 1.58 moles at800° C. 8.652 −91.232 H₂O, 1.62 moles at 800° C. 11.243 0 CO₂, 1.79moles at 1042° C. 21.824 0 N₂, 4 moles at 1526.3° C. 46.819 0 Total88.538 −91.232 Heat released and used to raise −18.281 steam during coalgasification Heat released and unused during +0.021 CaCO₃ decompositionHeat released and unused during −0.406 FeO Oxidation Total In = 198.514kcal, Total Out = 198.436 (this small difference represents cumulativecomputer errors) Hydrogen Energy = 54.2 of carbon ΔH of CombustionEnergy to Gas Turbine = 27.8% of carbon ΔH of Combustion Steam Raised =10.9% of carbon ΔH of Combustion Difference between the sensible heat ofthe output products and of the input reactants = ΔH of Combustion input

TABLE 3 Equilibrium for Gasification of C in the Presence of CaO at 800°C. and 7 atm. Equilibrium Gas Phase Composition H₂, Mole % = 41.10 H₂O,Mole % = 49.98 CO₂, Mole % = 3.238 CO, Mole % = 2.553 CH₄, Mole % =0.1288

TABLE 4 Equilibrium for Oxidation of FeO at 1526.3° C. and 7 atm 2Fe₂O₃= 4FeO + O₂, Equilibrium P_(O2) = 2.44 × 10⁻³ atm.

TABLE 5 Equilibrium for Decomposition of CaCO₃ at 1042° C. and 7 atmCaCO₃ = CaO + CO₂, P_(CO2) = 7.024 atm.

Table 1 shows the mass balance, Table 2 shows the heat/energy balance,and Tables 3, 4 and 5 show the equilibriums which occur in the threereactors. Specifically, Table 3 shows that the gasification reaction inthe first bubbling bed reactor produces wet, but otherwise nearly purehydrogen. Table 4 shows that equilibrium favors decomposition of theCaCO₃ in the second bubbling bed reactor, and Table 5 shows thatoxidation of the FeO to Fe₂O₃ is favored by equilibrium in the transferline reactor.

The heat/energy balance shown in Table 2 illustrates a minor portion ofthe energy content of the coal leaving the process as the differencebetween sensible heat of the products and reactants, i.e., only a minorportion of the input energy becomes waste heat. More than half of theenergy content of the coal leaves the process in the form of hydrogen,i.e., as energy to the gas turbine. Of the remaining energy content, aportion goes to raising steam (a lower value use) and only a smallamount becomes waste heat.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A process for converting coal into fuel cellquality hydrogen and sequestration-ready carbon dioxide using unmixedcombustion, comprising the steps of charging a first fluidized bedreactor with coal and high temperature steam which oxidizes a portion ofthe coal and produces substantially pure hydrogen gas and carbondioxide; circulating a mixture of solids among said first reactor andsecond and third reactors containing coal, calcium compounds present asCaO, CaCO₃, and mixtures thereof, and iron compounds present as FeO,Fe₂O₃ and mixtures thereof; reacting the CaO present in said firstreactor with carbon dioxide to form CaCO₃; reacting the CaCO₃ in saidsecond reactor to regenerate CaO while reacting coal and/or coal charwith Fe₂O₃ to form FeO and carbon dioxide; oxidizing the FeO present insaid third reactor to regenerate Fe₂O₃ and produce oxygen depleted airat an elevated temperature; and withdrawing substantially pure hydrogen,carbon dioxide and oxygen depleted air in separate streams from saidfirst, second and third reactors.
 2. The process according to claim 1,wherein the solids in said second reactor are fluidized using hightemperature steam and the solids in said third reactor are fluidizedusing compressed air.
 3. The process of claim 1, wherein the temperaturein the first reactor is in the range 650° C. to 850° C.
 4. The processof claim 1, wherein the temperature in the second reactor is in therange 1000° C. to 1100° C.
 5. The process of claim 1, wherein thetemperature in the third reactor is in the range 1400° C. to 1600° C. 6.The process of claim 1, wherein the pressure in the reactor system as awhole is in the range 2 to 20 atmospheres.
 7. The process of claim 1,wherein the ratio of calcium atoms (present as CaO/CaCO₃) to iron(present as FeO/Fe₂O₃) in said solids circulating between said fluidizedbeds is between 1.5 and
 2. 8. The process of claim 1, wherein the rateof solids circulation between the second and third reactors is such thatthe ratio of FeO entering the third reactor to oxygen in the airentering the third reactor is greater than 4 moles of FeO to 1 mole ofO₂ but less than 5 moles of FeO to 1 mole of oxygen.
 9. The process ofclaim 1, wherein the pressure of said superheated steam is about 7atmospheres.
 10. The process of claim 1, wherein said oxygen depletedair at elevated temperature is used to generate electricity by expandingthe heated air through a downstream gas turbine engine.